Every surface absorbs part of the sound that hits it. Hard surfaces like concrete absorb only 1–2%, while thick acoustic foam absorbs over 90%. The total absorption of a room, in sabins, controls its echo and reverberation.
How to use the Sound Absorption Coefficient Calculator
- Method
- Incident intensity (W/m²)
- Reflected intensity (W/m²)
- Surface 1 area
- Surface 1 coefficient α
- Surface 2 area
- Surface 2 coefficient α
- Surface 3 area
- Surface 3 coefficient α
- Surface 4 area
- Surface 4 coefficient α
- Surface 5 area
- Surface 5 coefficient α
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the method. For a room, enter the area and absorption coefficient of each type of surface.
Inputs explained
| Field | What to enter |
|---|---|
| Method | Choose one: From incident and reflected intensity, Total absorption of surfaces |
| Incident intensity (W/m²) | A number |
| Reflected intensity (W/m²) | A number |
| Surface 1 area | Units: m², cm², mm², km², in², ft² |
| Surface 1 coefficient α | A number |
| Surface 2 area | Units: m², cm², mm², km², in², ft² |
| Surface 2 coefficient α | A number |
| Surface 3 area | Units: m², cm², mm², km², in², ft² |
| Surface 3 coefficient α | A number |
| Surface 4 area | Units: m², cm², mm², km², in², ft² |
| Surface 4 coefficient α | A number |
| Surface 5 area | Units: m², cm², mm², km², in², ft² |
| Surface 5 coefficient α | A number |
What each result means
- Absorption coefficient α = 1 – [Reflected intensity (W÷m²)]÷[Incident intensity (W÷m²)]
- Total absorption = [Surface 1 area]×[Surface 1 coefficient α] + [Surface 2 area]×[Surface 2 coefficient α] + [Surface 3 area]×[Surface 3 coefficient α] + [Surface 4 area]×[Surface 4 coefficient α] + [Surface 5 area]×[Surface 5 coefficient α]
- Average absorption coefficient = [Total absorption]÷([Surface 1 area] + [Surface 2 area] + [Surface 3 area] + [Surface 4 area] + [Surface 5 area])
- Total surface area = [Surface 1 area] + [Surface 2 area] + [Surface 3 area] + [Surface 4 area] + [Surface 5 area]
Example values
How the main result changes when Incident intensity changes and everything else stays at the example values above:
| Incident intensity (W/m²) | Absorption coefficient α |
|---|---|
| 0.5 | 0.4 |
| 0.75 | 0.6 |
| 1 | 0.7 |
| 1.25 | 0.76 |
| 1.5 | 0.8 |
| 2 | 0.85 |
Formula
α = 1 − I_r / I_i · A = Σ S_i·α_i, ᾱ = A / Σ S_i
Worked example
Inputs — Method: Total absorption of surfaces; Surface 1 area: 48 m²; Surface 1 coefficient α: 0.02; Surface 2 area: 48 m²; Surface 2 coefficient α: 0.3; Surface 3 area: 84 m²; Surface 3 coefficient α: 0.05; Surface 4 area: 0 m²; Surface 4 coefficient α: 0; Surface 5 area: 0 m²; Surface 5 coefficient α: 0.
Results — Total absorption = 19.56 m² sabins; Average absorption coefficient = 0.1087; Total surface area = 180 m².
Key terms
- Sabin
- Unit of absorption, 1 m² of perfect absorber.
Frequently asked questions
What does α = 1 mean?
A perfect absorber, like an open window.
Does α depend on frequency?
Yes – most materials absorb high frequencies better.
What is the NRC?
Noise reduction coefficient: the average α at 250, 500, 1,000 and 2,000 Hz.
How do I reduce echo?
Add absorbing surfaces such as carpets, curtains or panels.